The present invention relates generally to lighting techniques. In particular, the present invention provides a method and device using a plasma lighting device. More particularly, the present invention relates to a plasma lamp developed for horticulture applications. The plasma lamp developed can be used for growth of various plants, including vegetables, fruits, flowers, algae, and other plants requiring light for growth.
Plant growth generally requires radiation in the 400 nm to 700 nm range of the spectrum (Photosynthetically Active Radiation, PAR). Photosynthesis is most efficient with red spectrum radiation where the photosynthetic quantum efficiency broadly peaks between ˜600 nm and 670 nm [McCree, Inada]. There is also a blue spectrum radiation peak at ˜450 nm that is ˜30% lower relative to the red spectrum peak. In addition to providing the energy source for the plant, radiation also stimulates various aspects of plant development, such as germination, flowering, stem length, etc. (photomorphogenesis). Red and blue radiation also drives these photomorphogenesis characteristics [Sager & McFarlane]. The optimum ratio of the amount of red to blue radiation required for plant growth varies over the development of the plant. For example, a higher blue component of radiation is often desirable during seedling growth, whereas a higher red content in the spectrum can be desirable for germination and flowering. One current lighting technique presently used in horticulture to provide blue light spectrum during the initial stages and red light spectrum during the flowering stage is to use fluorescent light bulbs for the blue spectrum and then later on switch to incandescent light bulb for the red spectrum. The problem with this approach is that neither of the two light sources can provide the high intensity per area needed in a number of horticulture application and the incandescent light sources are very inefficient. In another approach metal halide lamps are used for initial growth stage when the blue spectrum is needed and high pressure sodium lamps for the red spectrum stages. The problem with this approach is typically plants have to be physically relocated from one location to another to provide the different light spectrums and metal halides lamps are also inefficient. To eliminate the need for relocating the plants and the need for using metal halide lamps, a special HPS lamp has been developed that adds a small blue spectrum peak to the spectrum of HPS (HortiLux). However, the overall spectrum of this lamp is also inadequate for optimum plant growth and still the overall energy consumption is too high.
In yet another approach array of blue and red LEDs have been used to develop a light fixture having the blue and red spectrum peaks used for plant growth. However, due to do the array nature of the LEDs in the fixture, it is challenging to get a uniform intensity distribution over an area with a uniform light spectrum. So different plants (or parts of the same plant) get different spectrum of light depending on their location under the light source.
From the above, it is seen that improved techniques for horticulture lighting is highly desired.